The present invention relates to an optical information recording/reproducing optical system and an optical information recording/reproducing apparatus for recording information to and/or reproducing information from an optical disc based on a predetermined standard by irradiating an information recording layer of the optical disc with a laser beam, and particularly to an optical information recording/reproducing optical system and an optical information recording/reproducing apparatus suitable for information recording/reproducing for a high-recording density optical disc, such as BD (Blu-ray Disc).
There exist various standards of optical discs, such as CD (Compact Disc) and DVD (Digital Versatile Disc), differing in recording density, protective layer thickness, etc. Meanwhile, high-recording density optical discs (e.g., BD), having still higher recording density than DVD, are being brought into practical use in recent years to realize still higher information storage capacity. Incidentally, in this specification, the “optical information recording/reproducing apparatuses” include apparatuses for both information reproducing and information recording, apparatuses exclusively for information reproducing, and apparatuses exclusively for information recording, and the same thing can be said for the “optical information recording/reproducing optical systems”. In the following, the “optical system for optical information recording/reproducing apparatuses” is frequently referred to as an optical system of an optical pick-up.
When information recording or information reproducing for an optical disc is executed in the optical information recording/reproducing apparatus, undesired reflected light or scattered light, which are generated on optical surfaces of optical elements (e.g., an objective lens and a collimator lens configuring an optical system of an optical pick-up) may interfere with signal light, and thereby deteriorate the quality of the signal light which is used for information recording or information reproducing. For this reason, in many cases, a functional film, such as an antireflection film or an antistatic film for preventing adhesion of dust to an optical surface, is provided on an optical surface of an optical element (e.g., an objective lens) configuring an optical system of an optical pick-up.
Incidentally, laser light having a wavelength of approximately 400 nm (hereafter, referred to as “blue laser light”) is used for information recording and information reproducing for the high-recording density optical disc, such as BD. Since laser light having such a short wavelength has high photon energy and the laser light chemically affects material forming an optical element, the quality of the material forming the optical element tends to be changed when the laser beams passes through the optical element.
For this reason, if a resin lens coated with an antireflection film is irradiated, in an high temperature environment, with the laser light having a short wavelength and having a power density larger than or equal to a predetermined level, a minute change in shape of the coated optical surface of the resin lens occurs depending on the intensity distribution of the laser light with which the optical surface is irradiated, and thereby the optical performance of the resin lens (e.g., aberrations and optical efficiency) deteriorates.
Japanese Patent Provisional Publication No. 2005-251354A (hereafter, referred to as JP2005-251354A) suggests changing the resin base material of an optical element, as a measure against the above described problem.
More specifically, in JP2005-251354A, a technique in which resin having an alicyclic structure is used as the resin base material to reduce the degree of adhesiveness with respect to a functional film is suggested. However, it should be noted that the resin material is one of most important optical design parameters defining the optical performance of the optical element (i.e., the optical performance of an optical system of an optical pick-up). Therefore, it is not desirable to limit a selection range of resin materials. That is because the degree of design freedom reduces. In actuality, an optical configuration suggested in JP2005-251354A is not able to realize the optical performance required for an optical system of an optical pick-up for BD. In addition, the optical configuration suggested in JP2005-251354A is not able to achieve a sufficient light-resisting property.